1. Field of the Invention
This invention relates to belt filter presses for removing liquid from a mixture of liquid and solid material. In one aspect, the invention relates to an improved wedge section for a belt filter press.
2. Description of the Related Art
Belt filter presses are utilized to remove liquid from a mixture of liquid and solid material, leaving a relatively dry, solid xe2x80x9ccakexe2x80x9d for disposal or further processing. The belt filter press comprises a frame and an assembly of rollers that support and drive an upper continuous belt and a lower continuous belt that are in operable communication with each other. The belts are permeable to allow the extrusion of the liquid therethrough. The mixture is first placed on the lower belt, then xe2x80x9csandwichedxe2x80x9d between the upper and lower belts. The belts and the retained mixture then pass through a wedge section where the mixture is evenly distributed between the belts, and an initial volume of liquid is removed. The belts then pass through a series of progressively smaller diameter rollers where the retained mixture is compressed for further liquid removal. The belts are then separated and the dry xe2x80x9ccakexe2x80x9d is removed from the belts, generally by a scraping apparatus. The belts then pass through one or more belt washers, after which the process is repeated. The liquid from the extrusion and belt washing processes are collected for disposal.
The wedge section is generally planar, which is suitable for even distribution of the mixture between the belts. However, material passing over a planar wedge section will not be as effectively dewatered as material passing over a curved wedge section. Furthermore, the wedge section typically comprises a flat plate in full contact with the lower belt. Consequently, liquid that is extruded from the mixture must flow laterally to the edges of the belts in order to be removed. The drainage path defined by this lateral movement is appreciably longer than a drainage path perpendicular to the plane of the belts. The longer drainage path impedes the removal of liquid from the mixture.
The invention comprises an improved curved wedge section for a belt filter press for removing liquid from a mixture of liquid and solid material. The belt filter press comprises two endless filter belts disposed adjacent each other so that a portion of the belts travel together and converge towards one another in a curved wedge section through which a material is progressively compressed. The concavity of the wedge section is oriented toward gravity. The wedge section comprises a plurality of parallel-spaced belt supports comprising a rigid, polymeric material such as an ultra high molecular weight plastic or Nylotron. The supports are supported on parallel-spaced wedge support plates. The wedge section comprises a planar section that transitions into the curved section.
Belts containing the mixture to be dewatered pass over the curved wedge section prior to entering the roller section of the belt filter press. The curvature of the wedge section enhances the extrusion of water from the mixture prior to the belts entering the roller section.